1. Field of the Invention
This invention relates to a cleaning composition for removing stubborn mildew and other mycological stains from surfaces, the cleaning composition comprising an aqueous solution of an alkali metal hypochlorite, an alkaline builder, and a hypochlorite-compatible surfactant. More particularly, the invention concerns such a cleaning composition which is fluid foam having a particular combination of characteristics and a process for preparing the cleaning composition fluid foam.
2. Description of the Prior Art
Various aqueous mildew-removing products are available commercially for home use. Typically, the aqueous products contain a metal hypochlorite, an alkaline builder for maintaining the aqueous product at a pH of at least 11, and a surfactant. Such products typically are dispensed from plastic bottles equipped with hand-activated pumps for spraying the cleaner on a surface. The sprayed cleaning compositions usually are dispensed as liquids, short-lived foams, thickened liquids or gels.
Several aqueous alkali metal hypochlorite compositions for the removal of mildew stains, similar to those in the commercial products, are disclosed in patents, such as U.S. Pat. No. 5,281,280 (Lisowski et al), U.S. Pat. No. 5,290,470 (Dutcher et al), and U.S. Pat. No. 5,567,247 (Hawes). The present inventor found that although some of the known cleaning compositions remove mildew stains of mild intensity, none of the tested commercial products could remove long established, stubborn mildew stains unless cleaning was accompanied by vigorous scrubbing. In addition, almost all of the tested products lost cleaning efficiency with aging during storage.
The use of thickening agents to increase viscosity and change flow characteristics of aqueous hypochlorite-containing cleaning compositions in order to improve their cleaning ability is disclosed in various patents, as for example in U.S. Pat. No. 5,549,842 (Chang), U.S. Pat. No. 4,900,467 (Smith), U.S. Pat. No. 4,800,036 (Rose et al), and U.S. Pat. No. 4,337,163 (Schilp). The thickened liquids usually are disclosed for use as detergents in dish washers, sink drains and laundry washers, and some are also suggested for removing mildew.
Additives for stabilizing aqueous hypochlorite solutions against decomposition caused by temperature and other aging effects during storage are known. For example, U.S. Pat. No. 4,071,463 (Steinhauer) discloses for use as an alkali metal hypochlorite stabilizer, certain synthetic detergents (e.g., alkali metal alkyl sulfates and alkyl aryl sulfonates) and U.S. Pat. No. 4,898,681 (Burton), discloses calcium chelate of disodium ethylenediaminetetraacetic acid for such stabilizing use.
Although the known aqueous alkali metal hypochlorite cleaning compositions are useful for removing some mildew stains from surfaces, improvements are desired to greatly increase the cleaning efficiency of mildew stain removal so that scrubbing and/or high-pressure water-hosing normally is not required after the cleaning composition is used on a stained surface.
The present invention provides a cleaning composition for removing stubborn mildew from a surface normally without scrubbing. The cleaning composition is of the type that comprises an aqueous solution of an alkali metal hypochlorite, an alkaline builder that maintains the solution at a pH of at least 11, and a hypochlorite-compatible surfactant. The cleaning composition is a fluid foam that has, in combination, as measured by methods described hereinafter, (a) a precursor-solution relative viscosity of no greater than three, preferably in the range of 0.8 to 1.5, (b) a syneresis value in the range of 2 to 40%, preferably in the range of 10 to 30%, (c) a foam horizontal thickness half-life of at least 12 minutes, preferably at least 15 minutes, and (d) a vertical-surface clingability of at least 7 minutes, preferably at least 10 minutes. A preferred alkali metal hypochlorite is sodium hypochlorite which is present in a concentration in the range of 1 to 15 percent, preferably 3 to 10%, by total weight of the aqueous cleaning composition. A preferred alkaline builder is sodium hydroxide or potassium hydroxide. Preferably, the aqueous solution of alkali metal hypochlorite is free of undesired metal ions. Preferred compatible surfactants are a cocamine oxide, a sodium alkyl alkanoate and sodium dodecyl diphenyl disulfonate, present in a concentration range of 0.1 to 10%.
The invention also provides a method for forming the above-described cleaning composition fluid foam. The method comprises (a) preparing an aqueous solution of an alkali metal hypochlorite, preferably purified of unwanted metal ions, an alkaline builder that maintains the solution at a pH of at least 11, and a hypochlorite-compatible surfactant in a container and (b) vigorously agitating the solution in the presence of a gas with mechanical stirrers or by fluidic/pneumatic action of a fluid jet, preferably produced by a mechanical breakup actuator of an aerosol dispenser in the presence of propellant. Preferably, the foam is produced with a low-boiling hydrocarbon propellant in an aerosol dispenser made of materials compatible with the aqueous solution. Preferred propellants include propane, butane, isobutane and mixtures thereof in a concentration of 1 to 15%, preferably 3 to 10%, by weight of the aqueous cleaning composition. In the preferred aerosol dispenser, all parts and surfaces that contact the aqueous cleaning composition are of hypochlorite-compatible metal, rubber or plastic. Preferred plastic materials are polyethylene, polypropylene, nylon and polyester.